(1) Field of the Invention
The present invention relates to an ink jet recording head which jets ink in the form of a droplet from an ink nozzle by utilization of a piezoelectric effect.
(2) Description of the Related Art
An ink jet recording head for jetting ink in the form of a droplet from an ink nozzle by utilization of a piezoelectric effect has been well known in the art. Examples of such ink recording heads are disclosed in U.S. patent application Ser. Nos. 4,819,614 and 4,752,788.
FIG. 1 is a sectional view of a conventional ink jet recording head. As shown in FIG. 1, a plurality of concave-shaped ink cavities 52 are formed on one surface of a piezoelectric plate 51; the piezoelectric plate 51 made of piezoelectric materials is disposed between adjacent concave-shaped ink cavities; and a convex portion 53 made of piezoelectric materials is formed to conform the concave shape of the concave-shaped ink cavity 52. The top of the concave-shaped ink cavities is covered with a cover plate 54.
Each of the concave-shaped ink cavities 52 matching with the convex portion 53 comprises two deep grooves (b) for spacing the piezoelectric plate 51 and the convex portion 53 from each other and a shallow groove (a) between the deep grooves (b). An electrode 55 is provided on the bottom of the piezoelectric plate 51; and an electrode 56 is provided on the convex-portion 53. Also, a nozzle 57 is formed on the same surface of the piezo-electric plate 51 as the ink cavity to have the nozzle be coupled with the corresponding ink cavity.
When a voltage is applied across a selected pair of electrodes 55 and 56 in the ink jet recording head thus constructed, the convex portion 53 is deformed to change the volume of the ink cavity 51; as a result, ink in the ink cavity is jetted from the nozzle. The ink jet recording head, however, has the following drawbacks.
As was described with referring to FIG. 1, two deep grooves and one shallow groove are constructed in the piezo-electric plate 51; and the manufacturing cost of this piezo-electric plate 51 is relatively expensive. Particularly in the case when it is required to arrange ink cavities at a high density, the width of each groove (b) becomes as narrow as some .mu.m, and it is considerably difficult for the present manufacturing technique to form such ink cavities in a piezo-electric plate.
Further, between adjacent ink cavities is provided a bulkhead made of piezoelectric materials, accordingly, an electric field formed across the electrodes 55 and 56 may vibrate the bulkhead between the ink cavities. As a result, the volume of the adjacent ink cavity is changed due to cross-talk between the ink cavities. As a result, around a nozzle is stained with leakage of ink from the adjacent ink cavity, whereby the ink jetting direction is fluctuated.
The cross-talk between ink cavities may be prevented; however, since the convex-portion 53 and the bulkhead are provided as an integral unit, deformation of the convex portion 53 may cause deformation of the bulkhead. Consequently, effective ink jetting is hindered; otherwise, a high-speed response ability is retarded.
Further, the vibration of the convex portion 53 moves ink into the groove (b), the groove (b) for spacing the convex portion 56 and the bulkhead 51; therefore, ink jetting effect is degraded; or ink penetrates the convex portion 53 from its side walls, as a result of which a bulk resistance is lowered. Accordingly, a drop of voltage or an electrolysis of ink occurs. Also, a cavitation of ink occurs at the groove (b) due to the vibration of the piezoelectric plate, as a result of which effective jetting by utilization of pressure is hindered.